One Mast, One Sail

Wind crosses the water and presses against the people aboard. Hold up a larger surface and its pull becomes harder to ignore. Cloth that was easy to carry as a bundle can put quite a different demand on the hands holding its corners.

Attach that surface usefully to the boat and it can supply propulsion. The sail gathers a force from moving air and passes it into the hull through its supports and controls. The crew still has work to do, but the energy driving the boat need no longer come from repeated strokes of an oar.

A surface and its support

A pole-like member carrying or controlling a sail is a spar. The principal upright spar is the mast. Together, the sails, spars and their supporting and operating arrangements form the rig. The rig therefore describes a working assembly rather than only the shape of its cloth.

Pull on a rope and it carries tension, a load tending to stretch it. Push along a solid member and it carries compression, a load tending to shorten it or make it buckle sideways. Apply a load across a slender member and it can curve: this is bending. A mast holding a loaded sail can experience compression and bending together.

One way to support the mast is to lead tension members from it down to strong parts of the hull. A shroud supports it from the side. A stay commonly supports it in a fore-and-aft direction. These supports form its standing rigging. Their principal job is structural support, even when their tension can be adjusted.

Such a mast is stayed. An unstayed rig, also called a free-standing rig, carries the mast’s bending through the mast itself and its support in the boat, without conventional external stays and shrouds. For example, the mast can pass through a supporting bearing at deck level and have its lower end seated farther down in the hull. Those separated supports restrain its sideways movement and carry the bending load into the boat. A substantial mast and secure hull support can do that job; a slender mast needing external restraint cannot simply have its supports removed. The two arrangements distribute loads differently.

Whether a rig is stayed or unstayed does not specify its number of sails. Nor does it specify whether the mast is wood, metal or another material. Support, material and sail arrangement are separate properties that have to work together.

Up in the mast and rigging is aloft. Down near deck level or below is alow, a word encountered particularly in older descriptions. A load beginning aloft must reach structure capable of carrying it lower down. The route through each component and connection is the load path.

Bring the loads into the hull

Choose a stayed mast standing on the deck so that both support routes can be followed. This is one useful arrangement, rather than a model of the first sailing boat.

The mast’s lower end is its heel, also called its foot; mast foot can also name the base fitting. The mast step is the structural seat receiving that end and passing its load into the boat. In this deck-stepped example, the mast presses down on the step and the structure supporting that part of the deck.

An internal wall dividing the hull is a bulkhead. A structural bulkhead is designed to strengthen the hull or carry loads. Beneath our selected step, such a partition helps take the downward load into the surrounding hull. An ordinary partition does not acquire that capacity merely by occupying a convenient place.

Follow a shroud down the other route. It pulls on a chainplate, a strong attachment carrying the rigging load into the hull. In this example a metal strap is fastened through a structural partition. For this job the partition is a chainplate bulkhead. It can be separate from the bulkhead supporting the mast step; the important connection is that both eventually deliver their loads into the hull.

A chainplate bolt is one of the fastenings securing the attachment. The bolt passes through the strap and bulkhead, and a matching nut advances along its screw thread as it turns. Tightening the nut against the joined parts stretches the bolt slightly and clamps them together. Contact through the fastening and joined parts carries the chainplate’s pull into the supporting bulkhead.

The mast presses through its heel and step into deck support and hull. A shroud pulls through its chainplate, fastenings and supporting bulkhead into the hull. Other boats use different supporting arrangements and attachments, sized for their particular loads.

Corners, edges and a moving boom

Give the mast one triangular sail, with its forward edge supported near the mast and its lower edge extending aft. Its top corner is the head. Follow the forward edge downwards: that edge is the luff, ending at the lower forward corner, the tack. Along the bottom runs the foot, from tack to the lower after corner, the clew. The remaining edge, from clew back to head, is the leech.

Holding the tack locates the sail’s lower forward corner. Pulling at the head raises the sail. Controlling the clew changes how the sail is held aft. Here tack is a corner; when the boat later tacks, the word will name an action with its own explanation.

A boom is a spar extending aft from the mast to support or control the sail’s lower edge or clew. The end nearest the mast is its heel; the boom end is the outer end, away from the mast. In this arrangement the tack stays near the heel and the clew is held near the outer end.

The boom connects to the mast through an articulated joint, the gooseneck, or gooseneck fitting. Articulated means that connected parts can move relative to each other. The fitting allows the boom to swing sideways and, within the arrangement’s limits, rise or fall while remaining attached. Sail force can therefore move the boom without requiring the mast to turn with it.

In his 1889 handbook, E. F. Knight describes a boom held to the mast by wooden jaws, a forked end fitting around it, as well as an iron gooseneck. The wooden fitting bears around the mast as the boom moves; the metal joint provides articulation in the connection itself. Both keep the boom attached while allowing movement, using different materials and contact arrangements.

This principal sail is the mainsail, often shortened to the main. The name associates it with the principal mast. For the triangular sail in front of us, head, tack and clew are three distinct corners. Other sail geometries will alter some uses of these words, so the physical arrangement remains part of the definition.

Raise the head, control the clew

Take a rope securely attached to the sail’s head and lead it upwards, then turn it over a wheel near the top of the mast so its working end comes back down within reach. This is a halyard, also spelt halliard: a line used to raise or lower a sail or its supporting spar. For our mainsail, it is the main halyard.

The wheel has a groove guiding the rope. Such a wheel is a pulley; aboard it is commonly called a sheave, carried inside a housing called a block. A bearing supports the sheave while allowing it to turn. Pull down on the accessible end and the other end rises with the sail. The fixed block changes the direction of the pull. It does not, by that redirection alone, halve the ideal force required to lift the load.

There is friction, resistance to relative motion, where contacting surfaces rub. A turning sheave lets the rope travel without simply scraping around a fixed corner, although the rope bends and the wheel’s bearing still has losses. The actual effort therefore depends on more than the height of the mast. Arrangements using moving blocks can exchange force for a longer pull; that is a further step beyond this single fixed redirect.

Rope with a working job aboard is commonly called a line. A control line adjusts a sail, spar or other mechanism. The halyard controls height. A sheet controls a sail’s lower working corner, directly or through its boom. The mainsheet controls the mainsail: here it restrains the boom’s position sideways, and its downward pull can also restrain the boom from rising and change the sail’s shape.

Let the mainsheet out and the boom can swing farther from the centreline under the sail’s force. Draw it in and the boom is restrained closer. The useful setting depends on the direction of the air meeting the sail, which will change as the boat moves. Keeping the cloth merely raised is different from setting it to work.

To hoist the sail is to raise it. To set it is to put it into its working position and adjust it for use. To lower, or strike, it is to bring it down from that position. To stow it is to put it away and secure it for the conditions, rather than leave an unsecured bundle on the deck.

Halyards and sheets belong to the running rigging, the lines used to raise, lower, position and shape sails or move their spars. Standing rigging supports the mast; running rigging handles the working sail.

One mast and one principal sail

This elementary boat has one mast and one principal sail, without an additional sail ahead of the mast. Una rig describes a single-mast, single-sail arrangement. Cat rig is an overlapping name, usually associated with the mast placed well forward. Neither name alone guarantees a triangular sail or a free-standing mast.

The same 1889 handbook describes “Cat or Una” with a forward mast and a four-sided sail supported by an upper spar as well as a boom. Its use of una therefore includes a different sail outline from our triangular example. A first attestation is the earliest known written occurrence of a word. Knight supplies a dated use, whose priority has not been established; it dates the description, not the invention of the rig. The earliest surviving object is the oldest physical example presently known, a different kind of evidence from the earliest recorded word.

Our sail is boomed because a boom carries or controls its lower part. In a boomless arrangement the crew controls the sail without that conventional spar. For a simple example, attach the sheet directly to the clew, leaving the foot to span between its secured forward corner and that controlled after corner. The sheet now pulls on the cloth’s corner directly. Removing the boom changes how the lower corner is held and how the forces reach the boat.

Knight’s account belongs to a world in which sailing had already been practised for thousands of years. Move back to an Egyptian relief attributed to the third millennium BCE and sailors are represented handling and raising a sail. It preserves evidence of organised wind propulsion, although only part of the arrangement survives.

A large sail brings several making skills together. Joined cloth supplies the area; a shaped spar gives it height; ropes and attachments restrain its pull and carry it into the hull. The lifting line lets people raise or lower the surface while remaining below. More cloth becomes useful when its supports and connections can carry the increased load.

A modern reconstruction makes the work of producing that cloth tangible. In 2015, Denmark’s Viking Ship Museum was preparing a sail for its reconstruction of the Gislinge Boat, a Scandinavian working boat dating from about 1130 CE. Its planned ten-square-metre sail was to be sewn from five panels, long pieces of flax cloth. Flax is a plant fibre, prepared and spun (twisted together into thread) before the threads are woven into cloth. When one newly woven panel was wetted, it shrank more than expected; the remaining panels needed extra length to allow for that shrinkage. Producing the required sail area meant controlling the cloth’s finished dimensions as well as joining enough pieces. This was a present-day experiment in making an early medieval sail, distinct from the surviving Egyptian representation.

The galley model already encountered combines banks of oars with masts for sails. The two energy sources could serve different conditions on the same vessel. Wind might propel a boat without repeated human strokes; oars could still be useful when wind or confined water made the sail less helpful. The development adds a capability without requiring the previous one to disappear.

The hull can now receive force from the air through a complete assembly of cloth, spars, lines and structure. Its controls let the crew change that assembly while it is working. The next question comes from a moving boat: which wind should those controls answer, the wind over the water or the wind actually reaching the sail?